The present invention relates to a transmission apparatus for multiplexing a plurality of signals which are transmitted based on 8B/10B codes, such as Gigabit Ethernet signals or Fibre Channel signals. Gigabit Ethernet is a registered trademark and will be referred to as “Gigabit Ether” or “GbE” hereinafter.
In recent years, broadband data communications lines including the Internet become widespread for home-use purposes also, and the demand for high-speed lines is growing with a central focus on IP traffic. To meet this demand, traditional major technologies in wide area networks (WANs), such as the synchronous optical network/synchronous digital hierarchy (SONET/SDH) and asynchronous transfer mode (ATM), are replaced by the Gigabit Ethernet™, which is becoming important more and more in the marketplace because of its advantages as to high-speed performances and low costs.
A Gigabit Ether signal is in conformity to the rules compatible to Fast Ethernet rules, which are widely used in office-use local area networks (LANs), at the second layer (layer 2) in an open systems interconnection (OSI) reference model. The signal type is divided into two major categories: 1000BASE-X which uses light as a transmission medium, and 1000BASE-T which uses as its transmission media an unshielded twisted-pair (UTP) cable of the category 5 or higher. In particular, the former, 1000BASE-X, is popularized in the market while covering the aspects of from accessibility to trunk lines. One reason is its superiority in transport distance, and another reason is that optical elements are commercially available at relatively low prices.
However, in another aspect, such line demand growth accompanies risks as to the depletion of fiber-optic core lines for signal transmission via these broadband links. In the currently established network which is arranged to use Gigabit Ether signals, it is the big theme of a transmission apparatus on a branch line or a mainline to find an approach to maximizing the number of GbE lines per single optical fiber. To do this, the transmission device has experienced attempts to employ various types of multiplexing methods to thereby improve its communications line accommodation efficiency. However, in addition thereto, the transmission device is strictly required, from an aspect of maintenance services, to be a “transparent” transmission device with the absence of any influence upon the existing networks after installation of this device. Note here that the transparent transmission device refers to a transfer device which performs multiplex transmission without adding any modifications to user signals to be accommodated therein.
A prior known Gigabit Ethernet (GbE) multiplexing device is the one that is based on the existing SONET/SDH technology and is recommended upon multiplexing of GbE signals to employ a technique of the type having the steps of terminating an 8B/10B code upon receipt of it, converting 10-bit data into 8-bit data, extracting a media access control (MAC) frame, applying data processing for encapsulation to the MAC frame in accordance with a method as defined in the request for comments (RFC) 1662 of Internet Engineering Task Force (IETF) or in the telecommunication standardization sector of International Telecommunication Union (ITU-T) Recommendation X.86 or ITU-T Rec. G.7041, and multiplexing by mapping into a SONET/SDH signal(s). In the prior art GbE multiplex device, the 8B/10B code is terminated at a time whenever a GbE signal is received, so it suffers from a problem as to the lack of an ability to pass through the 8B/10B code between client devices.
In order to solve this problem, according to the ITU-T Recommendation G.7041, a scheme which is called the transparent generic framing procedure (GFP-T) has recently been standardized for the purpose of permitting transparent pass-through without terminating the code of a physical layer, such as an ordered set as defined in 8B/10B code. The goal of this approach is to transparently transport the ordered set by execution of “64B/65B encoding” which is a technique for coding into 65-bit data including the ordered set information in units of 64-bit blocks in the event of conversion to an 8-bit digital data stream.
Unfortunately, this technique is also based on the use of the existing SONET/SDH technology. Thus it becomes necessary to use high-priced parts and electrical/electronic circuits for performing the SONET/SDH processing while at the same time requiring high price components and large-scale circuitry for performing the 64B/65B-encoding/decoding process. This lessens the advantages of GbE systems, which are becoming the leading edge technology in recent years in place of the SONET/SDH networks owing to the capability of arranging flexible networks at low costs.
Additionally, in GFP-T, various types of ordered sets that are defined by 8B/10B codes are implemented by mere use of a new encoding/decoding scheme. Several information items must be transmitted in a rounded form, so this scheme is not able to realize complete or full transparency. For example, the number of errors is converted into the fact indicating “one or more errors are found.” Thus, the information concerning the quality of a layer 1, such as an indication of exactly how many errors were occurred, is terminated and disappeared here. This results in neglect of the functions as to the retention of physical line quality and the quality monitoring, which are important roles of a layer-1 device.
Upon installation of prior art GbE multiplexing devices, it does not come without accompanying some restraints which follow: (1) an ability is lost to automatically determine an optimal operation mode between user devices during auto-negotiation; (2) the switching in obstruction occurrence events is no longer performed in a proper way due to the lack of an ability to exchange obstruction information between the user devices; and (3) in case a preamble of MAC frame or the like is used for a unique function, such function becomes out of use.
In regard to the restraint (1), a maintenance serviceman is required to manually set up an operation mode irrespective of the fact that if the auto-negotiation is directly exchangeable between routers then the optimum operation mode is expected to be determined in an automated way. Regarding (2), a need is felt to realize it by use of an alternative means or realize by using auto-switching functionality at an upper-level layer or provide a limit such as installation only for those networks which are free from the need for backup or “spare” lines. As for (3), the present status is that the maintenance serviceman is forced to be patient with the restrictions on maintenance services, such as using none of the unique functions or installing a device which has its function alternative to the unique function. In addition, when installing the GbE multiplexer device in the event of modification or updating of a present network configuration, heavy workload is put in some cases to a service facility install division and/or maintenance group, such as a need to examine in advance whether various kinds of influences are present or absent.
It is therefore an object of this invention to provide a Gigabit Ethernet multiplexing apparatus with flexible expandability without having to take care of a variety of kinds of operation/maintenance restrains and influences upon services otherwise occurring due to the termination of 8B/10B code, such as a configuration ordered set of Gigabit Ether signal in the case of network configuration modification occurring due to variance of communication line demands, such as those stated supra.